Workshop 6– Multiple Water Accounts

WS6_Unsolved.7z

WS6_Solution.7z

Fact Sheet

LAKE TED HILLYER

Reservoir Information

Location: On the Purple River above the confluence with the Orange River.  

Purpose: Water Supply, Hydropower, Flood Control

Lake Data: Based on current sedimentation survey

Model Information

Networks

1. Basic Network – Contains a single reservoir (Upper) with a diverted outlet

Operations Sets

1. Basic – Minimum releases for water supply and hydropower
2. Hydropower High – Similar to Basic with much higher hydropower demand

Rules

1. Min Diversion – Constant year-round release through diverted outlet
2. Hydropower – Seasonally-varying power release through dam
3. Hydropower High – Larger seasonally-varying power release through dam

Water Accounts

1. Basic – Water supply account, 50% of con pool
2. HP_High – Water supply (50%) and hydropower (25%) accounts
3. DYMS – Water supply (50%) and hydropower (25%) accounts

Alternatives

1. Basic – Yield Analysis (account) run using Basic network and Basic water account set
2. HP_High – Yield Analysis (account) run using HP_High
3. NoAcHPHigh – Yield Analysis (whole reservoir) run using Hydropower High operations set
4. DYMS – Yield Analysis (account) run using Basic operations and DYMS accounts

Simulations

1. Full Period – Runs the extended historical period (1943 – 2015)

Workshop #6 – Multiple Water Accounts

In this workshop you will add additional water accounts to the water supply account you created in the last workshop. You will be able to investigate the interactions between the accounts and how having multiple accounts affects the reservoir operations and water supply firm yield. You will also see how using multiple accounts can help enforce priorities between purposes better than you were able to do during Workshop #4. Finally, you will look at how you can mitigate the effects of other purposes on water supply using Dependable Yield Mitigation Storage.

Part 1 – Multiple Accounts and Effects on Yield

• In HEC-ResSim open the watershed saved as '\Workshop6\Workshop6.wksp'
• Work in the 'Basic Network' network. Open the Reservoir Editor for 'Upper Res' and be sure the 'Basic' Operation Set is selected. The 'Min Diversion' and 'Hydropower' rules from Workshop #4 are present in all zones of the reservoir. Recall that the firm yield calculated with both rules active in that workshop was 1161 cfs, and 1361 cfs when the 'Hydropower' rule was removed from the 'Buffer' zone to simulate a reservoir operation plan or drought contingency plan that stopped power releases at low elevations. In Workshop #5, the yield using a single water account for water supply at 50% of the con pool was 908 cfs with hydropower releases also included without a dedicated water account.
• Open the Water Account Set Editor and select the 'Basic' water account set. The 'Water Supply' account you created in the last workshop is present at 50% of the conservation pool.
• Create a new 'Hydropower' account and assign it 25% of the conservation pool. Use the Accounts → New menu option to create the account.

• Go to the 'Basic' alternative in the Alternative Editor and assign the new hydropower account a full lookback storage of 281,750 ac-ft.
• Setup the Yield Analysis to calculate a yield for the 'Water Supply' account and related rule.
• Save all your changes and switch to the Simulation module. Activate and run the 'Basic' alternative in the 'Full Period' simulation after making sure to replace the simulation's version of the alternative from the base directory (right click on the alternative name).
• What is the new firm yield for the 'Water Supply' account? How does the new yield compare to previous workshops? What is your explanation?

• Next try increasing the hydropower demand. This has been done already and saved as the 'HP_High' alternative. In Workshop #4 without water accounts, this change would have significantly lowered the water supply yield. You can see this for yourself by running the 'NoAcHPHigh' alternative. This alternative is set to not use water accounts by setting the Water Account Set to NONE on the Operations tab in the Alternative Editor. This alternative also has the new higher hydropower demand in its own operation set 'Hydropower High'. What is the firm water supply yield for the 'NoAcHPHigh' alternative?

• Run the 'HP_High' alternative that re-introduces water accounts while keeping the increased hydropower release demand. What is the yield for this case? Can you explain why using accounts caused this change?

Part 2 – Dependable Yield Mitigation Storage

• Now you will explore the impact of reallocating storage to increase the size of the conservation pool. This will demonstrate the need for dependable yield mitigation storage (DYMS) to protect existing accounts from harm when reallocating storage.
• Imagine that a new water user in the basin leads to a reallocation of 120,000 acre-ft from flood to con storage. The existing water supply and hydropower water accounts stay the same size while the new user contracts for all of the reallocated storage. As we went over in the last lecture, we expect this reallocation to harm the existing accounts and require mitigation.
• Go back to the Network module, open the Reservoir Editor, and select the 'Basic' operation set on 'Upper Res'.
  • Duplicate this set (Operations → Duplicate…) and name the new set 'DYMS'.
  • Reallocate 3 ft of the pool from flood to con in this operation set by increasing the elevation of the 'Conservation' zone by 3 ft, to 1075 ft. This is an increase of 120,000 acre-ft.
  • Create a rule to release water for this new user. Add a new rule named 'New User Release' to all zones at the lowest model priority. Set this rule to release from 'Upper Res-Dam at Purple River'. Make it a function of Date and set the Limit Type to Minimum. Have the rule release 400 cfs year-round.
• Open the Water Account Set Editor and select the already created 'DYMS' account set.
  • Change this water account set to use the new operation set you just created. Choose the 'DYMS' operation set on the Reservoirs tab in the editor.
  •  Move to the Water Accounts tab. Previously you determined the storage in each water account as a percent of conservation storage. In this exercise we want to keep the two existing accounts the same size, but we increased the amount of conservation storage. You need to switch both water accounts to Specify Total Storage. Set the 'Water Supply' account to 563,500 acre-ft and the 'Hydropower' account to 281,750 acre-ft. This matches the sizes from the 'Basic' alternative you ran at the start of this workshop.

• • Create a water account for the new user called 'New User'. Attach the 'New User Release' rule to this account. Set the account storage to 120,000 acre-ft, matching the reallocated storage, and save your changes.
• Open the Alternative Editor and select the 'DYMS' alternative.
  • Set the Operation Set and Water Account Set to 'DYMS' on the Operations tab. Save the alternative, then move to the Lookback tab. Set the lookback storage for the new water account to a constant 120,000 acre-ft.
  • On the Yield Analysis tab, set the analysis type to Water Account Yield and select the 'Water Supply' water account and 'Min Diversion' water supply rule. Set the tolerances to 10 cfs and 1000 ac-ft and the search to Heuristic and Bisection. Save your changes.
• Return to the Simulation module. Add the 'DYMS' alternative to the 'Full Period' simulation. Select the Simulation → Edit… menu item then check the box next to the 'DYMS' alternative. Also check the Run New Extract box to ensure the time series for the 'DYMS' alternative are loaded into the simulation DSS file.

• Run the yield analysis for the 'DYMS' alternative. What is the firm yield for the water supply water account now? Why has it changed?

• Take some time to review some of the output time series. Open the HEC-DSS output file using the Tools → HEC-DSSVue… menu option. Time series from the 'DYMS' water account set have DYMS - * as the B-Part. The unallocated conservation storage is represented by the default water account, B-Part = UPPER-RES – DEFAULT WATER ACCOUNT. Look at the storages, outflows, and inflows for the different accounts. Try to make sure you understand what is happening.
• OPTIONAL: Mitigation in dependable yield mitigation storage is done by reallocating additional water from the flood pool and adding it to the original water account. Approximately how much additional storage needs to be added to the water supply account? What elevation does this put the guide curve at? Hint: Start with calculating the yield per ac-ft before and after the reallocation, then calculate an estimate for extra needed storage. Try that amount to start and manually iterate to get closer. You need to change the size of the water account, the guide curve elevation, and the lookback storage for the water account each iteration. You can use the spreadsheet from Workshop #3 to help calculate storage at different elevations or just figure it out to the nearest foot.